Unusual project, comments please...

[jethdub]

I am planning an unusual mixer project..(It's one hell of a learning curve, but that's the way I prefer to learn..) Part of which will consist of a 4-way crossover section (sallen key filters), each channel fed independantly from a virtual earth summing section. The sources (line input pre's) will be split and connected in parallel to all 4 mix sections. This configuration will allow me to mute each source off the mixbuss for each filter section, to control which frequency band of each source comes out of the other end. I guess I need to keep the parallel input impedance of the 4 mix sections high enough to avoid loading the source...any suggestions..?,

At the output end, the signals from the four filter sections will be summed once more, and I need level control at some point between the filter outs and the final mixers inputs.
I have been looking at the formulae for input impedance into a virtual earth summer, and I'm a bit confused about how placing a level pot infront of each channels mix resistor effects my calculations for source/input impedance (and therefore the feedback/gain resistor and the mix resistors themselves).. If this would complicate design too much I could buffer the volume pot before each mix channel, but I'd rather avoid the extra op-amp stage if I can. I'd also like to really understand the calculations! If anyone can give me, or point me towards a more detailed description of these design factors for a virtual earth sum stage I'd be grateful. I've searched hard but not found anything more than the basics....

Any thoughts I'd be very happy to hear them.. Thanks folks..Jeth

[Bazukaz]

Have you tried simulating your circuit ? Spice simulators really help a lot.

[jethdub]

Thanks for the suggestion, my problem is that i am living temporarily away from my base in the UK...I'm in a far corner of mexico where there is little to do and I've been putting thinking time into this project in order to fill my spare time. I don't really have access to the resources to do as much research as I would like, and I don't have my own computer- Otherwise I'd love to work it all out for myself, but I'm hoping I can use the forums to help me develop this idea without such resources...
I'm a relative beginner and at the stage of moving on from building standard circuit blocks toward trying to complete a system design, it's a steep learning curve as I said, but it throws up questions which can move my knowledge on...if I can only find the answers! There seems to be an information wilderness at this stage of learning...